The present invention relates generally the reaction that occurs between glucose and proteins and, more particularly, to the inhibition by various agents of the reaction of nonenzymatically glycosylated proteins leading to advanced glycosylation end products. The nonenzymatic browning reaction which occurs in the oral cavity results in the discoloration of teeth. Presently used anti-plaque agents accelerate this nonenzymatic browning reaction and further the staining of the teeth.
The appeal of a perfect smile composed of pearly-white teeth is undeniable. Many dollars are spent to achieve this appearance, and the natural discoloration which occurs on the tooth surfaces often becomes quite noticeable in many individuals. Tooth discoloration is also greatly accelerated in most individuals who use certain anti-plaque agents to prevent oral disease. The purpose of the present invention is to provide a method and agents for preventing the discoloration which occurs on the tooth surface as a result of nonenzymatic browning, both naturally and as a result of the use of anti-plaque agents. As used herein, "tooth" and "teeth" refer to both naturally occurring and artificial teeth, artificial tooth surfaces and restorations. Dental caries, gingivitis and periodontal disease are widespread and affect nearly all individuals to some extent cosmetically, medically, and financially. These conditions arise from the action of certain microorganisms, principally bacteria, which colonize surfaces in the mouth and whose action lead to demineralization of bone, resulting in caries, and chronic irritation and infection of gum tissue (gingivitis) especially in pockets surrounding the teeth, leading to periodontal disease. The results of both processes can be painful, disfiguring and psychologically debilitating.
The development of tooth and gum disease is a complex process involving contributions from the tooth and gum surface, components and properties of saliva, diet, and the numerous species of bacteria present in the mouth, as well as many other factors. Generally, incubation of a newly cleaned tooth surface in the mouth initially results in the deposition on the surface of a material called pellicle, which is composed of protein and polysaccharide derived from saliva and bacterial cells. As colonizing bacteria grow, they produce a polysaccharide from the decomposition of food sugars. This polysaccharide favors the attachment of the bacteria to the tooth surface and also favors mineralization of calcium salts from saliva in the pellicle. As the process continues, the bacterial mass known as plaque becomes a focus for demineralization of bone and irritation of tissues. Acids produced by bacteria during food sugar fermentation dissolve bone, and the plaque mass prevents buffers in saliva from neutralizing these acids. The result is dental caries. The bacteria in plaque and those residing in pockets surrounding teeth produce endotoxin and other well-known bacterial products which are intensely irritating to tissues and cause the tissues to react resulting in recession of gum tissue, demineralization of bone, and localized irritation. One of the consequences of long-term exposure of proteins in the pellicle and plaque to sugars in the mouth is the process of nonenzymatic browning, which results in discoloration of the tooth surface. Nonenzymatic browning, also known as the Maillard reaction, has been well studied by food chemists since it is responsible for the brown color which forms during the cooking and long-term storage of foods. In this reaction, amino groups in food proteins and other molecules react with sugars to form covalent adducts which undergo rearrangements and result in highly polymerized, colored products. While this process is well-known in food, only recently was its significance realized as concerns the human body and consequences of the long-term exposure of glucose to amino groups on proteins and other macromolecules in the body. The Maillard reaction in vivo has been studied extensively in the last few years and nonenzymatic browning and cross-linking of proteins in vivo has been shown to be an important mechanism by which the sequelae of diabetes and aging arise (see M. Brownlee et al., "Nonenzymatic glycosylation and the pathogenesis of diabetic complications," Annals of Internal Medicine, 101, pp. 527-537 (1986). Elevated glucose levels in diabetes leads more rapidly to consequences involving permanent cross-linking of proteins, yet the normal glucose levels in non-diabetics eventually leads to the same complications.
Methods to prevent nonenzymatic browning in vivo with agents such as aminoguanidine and other inhibitors have been studied (Brownlee et al., "Aminoguanidine prevents diabetes-induced arterial wall protein cross-linking," Science, 232, pp. 1629-1632 (1986), Cerami et al., U.S. patent application Ser. No. 798,032; and U.S. patent application Ser. No. 07/119,958.
For many years certain agents have been tested and used to reduce the extent of oral diseases including dental caries, gingivitis and periodontal disease. Regular brushing and flossing apparently are inadequate, at least to the extent practiced by the average individual. Abrasive agents such as silica have been incorporated into toothpastes to attempt to physically remove plaque by enhancing the effectiveness of brushing. Anti-microbial agents have been formulated in oral rinses for regular use to kill bacteria in the mouth. Such agents include sanguinarine, an extract from the bloodroot, which kills certain oral bacteria; certain forms of active peroxide for killing microorganisms; rinses containing alcohol and other ingredients; and, more recently, a class of cationic anti-microbial agents with remarkable anti-plaque properties.
These latter agents, the cationic antiseptics, include such agents as alexidine, cetyl pyridinium chloride, chlorhexidine gluconate, hexetidine, and benzalkonium chloride. Many have been tested for efficacy but one, chlorhexidine gluconate, has shown the greatest promise as an anti-plaque agent of low toxicity (see Hull, "Chemical inhibition of plaque," J. Clin. Periodontol., 7, pp. 431-432 (1980); Bain, "Chlorhexidine in dentistry: A review," New England Dent. J., 76, pp. 49-54 (1980); Tonelli et al., "Chlorhexidine: A review of the literature," J. West. Soc. Periodent., 31, pp. 5-10 (1983) and has recently become available in the United States in a prescription formulation known as Peridex.RTM. which contains 0.12% chlorhexidine gluconate in a solution of water, alcohol, glycerine, flavoring, sweetening and coloring agents. Chlorhexidine gluconate, formulated in such a rinse, shows excellent promise as an anti-plaque agent but it has been found to possess an unfortunate side effect: staining of teeth. While this side effect is of no medical concern, it is an extreme psychologic concern because stained teeth look ugly and project an undesirable image to others. Tooth staining by chlorhexidine and other anti-plaque agents apparently results from the enhancement of the Waillard reaction. Nordbo, J. Dent. Res., 58, p. 1429 (1979) reported that chlorhexidine and benzalkonium chloride catalyze browning reactions in vitro. Chlorhexidine added to mixtures containing a sugar derivative and a source of amino groups underwent increased color formation, attributed to the Maillard reaction. It is also known that use of chlorhexidine results in an increased dental pellicle. Nordbo proposed that chlorhexidine resulted in tooth staining in two ways: first, by increasing formation of pellicle which contains more amino groups, and secondly, by catalysis of the Maillard reaction leading to colored products. Thus, there exists a need for preventing the staining caused by chlorhexidine gluconate and other cationic mouth rinses which will not interfere with their potent anti-microbial and resulting anti-plaque activity.